The Purple Pig Gets MSD Electronic Fuel Injection - The Atomic Age

I say I’m a points and carburetor kind of guy because in my mind I figure if they go wrong I can fix ’em at the side of the road. However, they both require fiddling with to get an engine to run right, and my attitude may have more to do with my reluctance to accept change than any rational reasoning! I drive a late-model truck most days, and have yet to futz with the ignition or fuel delivery systems, so I figured maybe it was time to jump into the 21st century with one of my projects.

2/311 While there was absolutely nothing wrong with the 4160-style Quick Fuel four-barrel that has been on the engine since it was built, we’ve been keen to install EFI on one of our projects for a while now.

A meeting with Todd Ryden from MSD Performance at the beginning of the year resulted in a conversation about the company’s new Atomic EFI (electronic fuel injection) system. Before long, we were discussing stopping off at MSD’s facility in El Paso, Texas, en route to the Lonestar Round Up in April, to swap out the four-barrel carburetor on my Project Purple Pig ’49 Chevy for the new Atomic. This would provide some real world data and a great comparison between the carb and EFI out on the road. Well, best laid plans and all that, while the ’49 did get to EL Paso, it was on a trailer. I got it driving the weekend before our intended departure, but wasn’t comfortable driving it almost 3,000 miles across the desert and back with no testdrives apart from a few laps around the block. So, unfortunately, the comparisons will have to wait for when I re-install the carb and do some testing.

The benefits of EFI include faster startup, better driveability, cleaner idling, and potentially more horsepower. Right away, after our install, the improvement in startup was evident, with absolutely no need to touch the gas pedal, even on cold starts.

3/312 Here’s what you get in the Atomic EFI kit: the throttle body (TB) with integral ECU, throttle body harness, power module (PM), power module harness, handheld monitor, O2 sensor and harness, 4-foot CAN extension, and gaskets. In the bag are a coolant temp sensor, O2 bung and plug, PM mounting hardware, grommets, and a 4G micro SD card.

The Atomic EFI is designed to bolt on to any square-bore, four-barrel intake, including common 4150 and 4160 designs, and will therefore fit any engine for which such an intake, or adaptor, is available. It shouldn’t be installed on engines making less than 100 or more than 525 hp, though there’s an optional high-horsepower pump kit that will support 620 hp. It also cannot be used in dual-quad applications, or with any power adders or alternative fuels at this time. That’s not to say MSD won’t alter this in the future. It can, however, be used with returnless fuel systems if required, though you’ll need the Master Kit, which includes a pulsing fuel pump, fuel filter, and fuel lines.

The ’49 already has an Aeromotive pump-in-tank fuel system, with a return line, so we only required the throttle body kit. While on the subject of fuel delivery, MSD recommends you don’t use hard lines for your entire fuel system. Factory EFI systems have suppressors built into the ends of the fuel rails to counteract the pulsing of fuel in the lines, and rubber hoses tend to do a similar job. While our Chevy has hard lines under the car, braided line is used from the tank to just ahead of the rearend, and from the bottom of the firewall up to the regulator, which should suffice. Plus, as it’s a return system, pulsing is reduced anyway.

What makes the Atomic EFI so user-friendly is the fact that it is a direct swap for a four-barrel, with the throttle cable and kick-down or TV cable simply swapping over from one to the other, and there are only eight wires to connect. The Atomic requires a 12V square-wave signal to use as a trigger. This is the same signal that most aftermarket tachometers require and is provided by a typical CD ignition, such as an MSD 6A. Also, MSD’s Ready-to-Run distributors or their HEI Module all provide a 12V square-wave signal through a separate tach output wire.

4/313 To simplify the installation, we’d welded the wideband O2 bung into the driver side exhaust, just below the header flange, prior to our visit to MSD. We also installed the sensor, though it should be noted a vehicle shouldn’t be driven with the sensor installed and not hooked up.

The Atomic also has the capability to control ignition timing. This requires an MSD Ignition Control as well as one of their standard distributors. While at MSD, they converted our regular HEI distributor to work with the Atomic by replacing the control module with one of their HEI modules. This module is available separately.

You may wonder how much current this system takes to operate. If you have two engine cooling fans and both are on, the fuel pump is at full capacity, the injectors are at their maximum, and the input voltage is around 10 V, the system can draw as much as 30 amps. Normal operation is approximately 14-18 amps. Note this is with two fans, it’s not the EFI alone that’s drawing this current. When our single fan switched on, we noticed the engine stumbled a little at idle, though with the alternator disconnected it was fine. This pointed to the fact that our alternator isn’t rated for a high enough output (plus it was running at idle speed), and considering the Chevy has an electric brake booster, an air ride system, A/C, and electric exhaust cutouts, along with the usual electrical systems in a car, we’ll be sourcing a 140-amp alternator in short order!

The main appeal of this system for us is that not only was the install easy and straightforward, but come time to start the engine for the first time, there’s no throttle configuration to contend with, and no fuel map tuning. Simply input some basic engine data into the handheld controller, then let the system self-learn. The throttle position sensor (TPS) is an automatic self-calibrating, non-contact sensor integral to the ECU, which itself is integral to the throttle body, reducing wiring. As well as the TPS, the MAP, IAT, and fuel pressure sensors are also all incorporated into the throttle body, meaning the only sensors that require connecting are the coolant temperature and O2 sensors (both are supplied with the kit). The latter is the only fabrication required for the entire install, as the O2 bung has to be welded into the exhaust system.

5/314 We routed the wiring for the O2 sensor alongside the brake lines, ensuring they were as far as possible from the exhaust and steering. The connection was made on the inside of the chassis and secured. The wiring from this connector was then routed discretely up to the power module, which we’d mounted behind the dash.

If you want to find out more about the Atomic EFI, check out the product-specific website at www.atomicefi.com, which not only has all the details you could wish to know, but also a forum, answers to frequently asked questions, and even an install video showing a returnless fuel system install. Meanwhile, here’s how the MSD crew set about converting the Purple Pig.